Collapse of polymer brushes grafted onto planar ... - Wageningen UR

CAPILLARY-INDUCED FORCES BETWEEN PARTICLES IN POLYMER SOLUTIONS NEAR
PHASE SEPARATION
M. Olsson, F. Joabsson, P. Linse, L. Piculell
Physical Chemistry 1, Center for Chemistry and Chemical Engineering,
Lund University, P.O. Box 124, S-221 00 Lund
email: Martin.Olsson@fkem1.lu.se
ABSTRACT
Capillary-induced phase separation (CIPS) leads to a long-ranged attractive force between two surfaces
immersed in a bulk solution. The formation of a new phase in the gap between the surfaces is driven by a
lower surface energy for the new (capillary) phase compared to the bulk phase. The decrease in free energy
is larger at shorter separations between the particles than for longer ones. An important condition for CIPS to
arise is that the particle-free solution has to be close to phase separation.
CIPS forces are known to affect particle aggregation in mixed solvents and in polymer blends as well as
protein aggregation in biological membranes. We have instead looked at polymer solutions with added
colloidal dispersed particles both experimentally and theoretically. Previous surface force measurements
have showed that CIPS occurs in mixed polymer solutions as well as in quasi-binary polymer solutions [1,2].
A complementary experimental study [3] for the mixed polymer system displays phase separation at
compositions far into the one-phase area for the original phase diagram, when colloidal particles are added.
To investigate more generally the parameters affecting CIPS for the mixed polymer system, a theoretical
mean-field lattice study has been done [4]. This study shows that CIPS occurs close to phase separation for
the system and is affected by parameters like the molecular weight of the polymer, the affinity of the polymer
to the surface, the composition of the sample and the distance between the particles. A recent study [5]
shows that CIPS can also appear in quasi-binary solutions. This has also been shown experimentally.
References
1. Freyssingeas, E., Thuresson, K., Nylander, T., Joabsson, F., Lindman, B., 1998. Langmuir 14, 5877-5889.
2. Wennerström, H., Thuresson, K., Linse, P., Freyssingeas, E., 1998. Langmuir 14, 5664-5666.
3. Joabsson, F., Calatayu, A., Thuresson, K., Piculell, L., submitted. Journal of Physical Chemistry B.
4. Joabsson, F. and Linse, P. “Capillary-Induced Phase Separation in Mixed Polymer Solutions. A Lattice
Mean-Field Calculation Study”, manuscript.
5. Olsson, M., Linse, P., Piculell, L. “Capillary-Induced Phase Separation in Binary and Quasi-binary Solutions.
A Lattice Mean-Field Calculation Study”, manuscript.